Cyclic process for producing taurine

ABSTRACT

There is disclosed a process for producing taurine from ammonium isethionate by the ammonolysis of alkali isethionate in the presence of alkali ditaurinate or alkali tritaurinate, or their mixture, to inhibit the formation of byproducts and to continuously convert the byproducts of the ammonolysis reaction to alkali taurinate. Alkali taurinate is reacted with ammonium isethionate to obtain taurine and to regenerate alkali isethionate. The production yield is increased to from 90% to nearly quantitative. The ammonolysis reaction is catalyzed by alkali salts of hydroxide, sulfate, sulfite, phosphate, or carbonate.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of co-pending applicationSer. No. 15/268,071, filed on Sep. 16, 2016, which is incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a cyclic process for the production oftaurine from ammonium isethionate in a high overall yield (i.e., greaterthan 90% to nearly quantitative) by carrying out the ammonolysisreaction of alkali isethionate to alkali taurinate in the presence of amixture of alkali ditaurinate and alkali tritaurinate, followed byreacting with ammonium isethionate.

BACKGROUND OF THE INVENTION

Taurine can be referred to as 2-aminoethanesulfonic acid and is one ofthe amino sulfonic acids found in the tissues of many animals. Taurineis an extremely useful compound with beneficial pharmacological effects,such as detoxification, fatigue-relief, and nourishing and tonifyingeffects. As a result, taurine finds wide applications as an essentialingredient for human and animal nutrition.

Taurine is currently produced in an amount of over 60,000 tons per yearfrom either ethylene oxide or monoethanolamine. At the present time,most taurine is produced from ethylene oxide, following a three-stepprocess: (1) the addition reaction of ethylene oxide with sodiumbisulfite to yield sodium isethionate; (2) the ammonolysis of sodiumisethionate to yield sodium taurinate; (3) the neutralization with anacid, i.e., hydrochloric acid and, preferably, sulfuric acid, togenerate taurine and inorganic salts.

Although the ethylene oxide process is well established and widelypracticed in commercial production, the overall yield is not very high,less than 80%. Moreover, the process generates a large waste stream thatis increasingly difficult to dispose of.

The first stage of the ethylene oxide process, the addition reaction ofethylene oxide with sodium bisulfite, is known to yield sodiumisethionate in high yield, practically quantitative, as disclosed inU.S. Pat. No. 2,820,818 under described conditions.

Therefore, the problems encountered in the production of taurine fromthe ethylene oxide process arise from the ammonolysis of sodiumisethionate and from the separation of taurine from sodium sulfate.

U.S. Pat. No. 1,932,907 discloses that sodium taurinate is obtained in ayield of 80%, when sodium isethionate undergoes ammonolysis reaction ina molar ratio of 1:6.8 for 2 hours at 240 to 250° C. U.S. Pat. No.1,999,614 describes the use of catalysts, i.e., sodium sulfate, sodiumsulfite, and sodium carbonate, in the ammonolysis reaction. A mixture ofsodium taurinate and sodium ditaurinate is obtained in a yield as highas 97%. However, the percentage for sodium taurinate and sodiumditaurinate in the mixture is not specified.

DD 219 023 describes detailed results on the product distribution of theammonolysis reaction of sodium isethionate. When sodium isethionateundergoes the ammonolysis reaction with 25% aqueous ammonia in a molarratio of 1:9 at about 280° C. for 45 minutes in the presence of sodiumsulfate and sodium hydroxide as catalyst, the reaction products comprise71% of sodium taurinate and 29% of sodium di- and tri-taurinate.

WO 01/77071 is directed to a process for the preparation of ditaurine byheating an aqueous solution of sodium taurinate at a temperature of 210°C. in the presence of a reaction medium. A mixture of sodium taurinateand sodium ditaurinate is obtained.

It is therefore concluded from the foregoing references that theammonolysis of sodium isethionate invariably yields a mixture of sodiumtaurinate, sodium ditaurinate, and sodium tritaurinate. The percentageyield of sodium taurinate has not been more than 80%.

In order to obtain taurine from sodium taurinate, U.S. Pat. No.2,693,488 discloses a method of using ion exchange resins involving astrongly acid ion exchange resin in hydrogen form, and then an anionexchange resin in basic form. This process is complicated and requiresthe use of a large quantity of acid and base to regenerate the ionexchange resins in each production cycle.

On the other hand, CN101508657, CN101508658, CN101508659, andCN101486669 describe a method of using sulfuric acid to neutralizesodium taurinate to obtain a solution of taurine and sodium sulfate.Crude taurine is easily obtained by filtration from a crystallinesuspension of taurine after cooling. However, the waste mother liquorstill contains taurine, sodium sulfate, and other unspecified organicimpurities, which are identified as a mixture of sodium ditaurinate andsodium tritaurinate.

U.S. Pat. No. 9,428,450, U.S. Pat. No. 9,428,451, U.S. Pat. No.9,573,890, and U.S. Pat. No. 9,598,357 overcome some of the problems inthe known ethylene oxide process by converting the byproducts of theammonolysis reaction of alkali isethionate, alkali ditaurinate andalkali tritaurinate, into alkali taurinate. The overall yield of thecyclic process for producing taurine from sodium isethionate isincreased to from 85% to nearly quantitative.

CN 104945289A and CN 105732440A describe recycling of the mother liquor,which contains sodium ditaurinate and sodium taurinate, during theammonolysis of sodium isethionate in the production of taurine toincrease the yield and to reduce discharge of waste.

U.S. Pat. No. 8,609,890 discloses a cyclic process of using isethionicacid or sulfur dioxide to neutralize alkali taurinate to producingtaurine and to regenerate alkali isethionate. U.S. Pat. No. 9,108,907further discloses a process of using isethionic acid prepared fromethanol to neutralize alkali taurinate to regenerate alkali isethionate.The aim is to reduce or eliminate the use of sulfuric acid as an acidagent in the production of taurine.

U.S. Pat. No. 9,061,976 discloses an integrated production scheme byusing sulfur dioxide as an acid and by converting the byproducts of theammonolysis reaction, alkali ditaurinate and alkali tritaurinate, toalkali taurinate. The overall production yield is increased to greaterthan 90% and alkali sulfate is eliminated from the production process.One drawback of this process is the use of gaseous sulfur dioxide, whichimparts a slight smell on the product. Another significant drawback isthat the taurine product from this process may contain trace amount ofalkali sulfite which could be an allergen for certain people.

U.S. Pat. No. 9,593,076 discloses a cyclic process for producing taurinefrom isethionic acid in a high overall yield of greater than 90% tonearly quantitative, while generating no inorganic salt as byproducts.Similarly, CN 106008280A describes the use of isethionic acid toneutralize sodium taurinate and to regenerate sodium isethionate.However, the starting material, isethionic acid, is difficult to obtaincommercially and is produced by a costly process of bipolar membraneelectrodialysis of alkali isethionate.

CN 101717353A describes a process of preparing taurine by (1) reactingethylene oxide with ammonium sulfite to yield ammonium isethionate andammonia; (2) ammonolysis of the obtained product to ammonium taurinate;(3) acidifying with sulfuric acid to afford taurine. However, repeatedattempts fail to produce any taurine under disclosed conditions.

It is an object of the present invention to overcome the disadvantage ofthe known processes for the production of taurine and to provide, inaddition, advantages, which will become apparent from the followingdescription.

It is another object of the present invention to disclose a process forthe production of taurine from ammonium isethionate in a high overallyield (i.e., greater than 90% to nearly quantitative) without generatingany inorganic salt as byproduct.

The starting material, ammonium isethionate, can be readily andeconomically produced by reacting ethylene oxide with ammonium bisulfiteaccording to prior art, e.g., U.S. Pat. No. 5,646,320 and U.S. Pat. No.5,739,365.

According to the process of the present invention, a solution of alkaliisethionate or regenerated alkali isethionate, alkali ditaurinate, andalkali tritaurinate is mixed with an excess ammonia and is subjectedcontinuously to the ammonolysis reaction to form a mixture of alkalitaurinate, alkali ditaurinate, and alkali tritaurinate, in the presenceof one or more catalysts. After ammonium isethionate is added to theammonolysis solution, excess ammonia is removed to obtain a crystallinesuspension of taurine in a solution of alkali isethionate, alkaliditaurinate, and alkali tritaurinate. Upon the solid-liquid separationof taurine, the mother liquor is directly recycled to the ammonolysisstep.

The advantage of using ammonium isethionate as a starting materialbecomes apparent in that no isolation of alkali salt as a byproduct isnecessary after the separation of crystalline taurine from the motherliquor containing alkali isethionate, alkali ditaurinate, and alkalitritaurinate. Moreover, the final product, taurine, does not contain anyinorganic salt, such as alkali sulfate or alkali halide, as impurity.

DESCRIPTION OF THE INVENTION

The present invention relates to a cyclic process for the production oftaurine from ammonium isethionate in a high overall yield of greaterthan 90% to nearly quantitative without generating any inorganic salt asbyproduct.

The starting material, ammonium isethionate is produced by reactingethylene oxide with ammonium bisulfite according to the followingequation:

Ammonium isethionate, produced in a solution, can be used directly forthe production of taurine. Preferably, ammonium isethionate is purifiedby concentrating the solution to obtain crystalline materials. Whensolid ammonium isethionate is used in the production of taurine, thequality of taurine produced is improved and almost no purge of motherliquor is required from the cyclic process.

The process according to the present invention starts with mixing asolution of alkali isethionate or regenerated alkali isethionate, alkaliditaurinate, and alkali tritaurinate, with an excess of ammonia. Thepresence of alkali ditaurinate and alkali tritaurinate in the reactionsolution inhibits the formation of byproducts, increases the productionyield, and greatly reduces or eliminates the waste discharge from theproduction process. The alkali metals are lithium, sodium, or potassium.

The ammonolysis reaction is carried out at a temperature from 160° C. to280° C. under the pressure from autogenous to 260 bars for 1 to 6 hours.

After the ammonolysis reaction, excess ammonia is dispelled from thereaction solution and reclaimed for reuse. Ammonium isethionate is addedto the ammonolysis solution before or after the removal of excessammonia to react with alkali taurinates to yield alkali isethionate andammonium taurinate.

Ammonium taurinate is decomposed to taurine by heating and removingammonia from the solution. The temperature for decomposing ammoniumtaurinate is from 75° C. to 150° C., preferably from 90 to 120° C., mostpreferably from 95 to 110° C. Removal of ammonia released from thedecomposition of ammonium taurinate can be carried out under reduced,normal, or increased pressure.

The amount of ammonium isethionate in relation to alkali taurinate inthe ammonolysis solution can be from 0.1 to 10 on the molar basis.Preferably, the molar ratio is from 0.5 to 1.5, more preferably from 0.9to 1.1, and most preferably from 0.95 to 1.05. When the ratio is lowerthan the equivalent, the final pH after ammonia removal tends to behigher than 7 and more taurine will remain in the solution. When theratio is greater than equivalent, the final pH is in the desirable rangeof 5 to 6, but additional alkali hydroxide will be consumed during theammonolysis stage.

The reaction of alkali taurinate formed in the ammonolysis stage withammonium isethionate proceeds according to the following equation:

After complete removal of ammonia, the strongly basic solution becomesneutral to yield a crystalline suspension of taurine in a solution ofalkali isethionate, alkali ditaurinate, and alkali tritaurinate. Thefinal pH can also be fine-adjusted with the mixed acids of isethionicacid and ditaurine, produced by the bipolar membrane electrodialysis ofthe mother liquor containing alkali isethionate and alkali ditaurinate.The initial suspension is optionally concentrated, then cooled tocrystallize taurine in a solution of alkali ditaurinate, alkalitritaurinate, and alkali isethionate. Taurine is obtained by means ofsolid-liquid separation.

After separation of taurine, the mother liquor, containing regeneratedalkali isethionate, alkali ditaurinate, and alkali tritaurinate, issaturated with ammonia and is subjected to the ammonolysis reaction.

It becomes apparent that alkali in the reaction system is continuouslyrecycled in the process and only ammonium isethionate is transformed totaurine. The net reaction of the cyclic process is:

Useful and effective catalysts for the ammonolysis reaction are foundamong the alkali salts of hydroxide, carbonate, bicarbonate, hydrogensulfate, sulfate, bisulfite, sulfite, nitrate, phosphate, chlorate, andperchlorate. Such salts are sodium hydroxide, lithium hydroxide,potassium hydroxide, lithium carbonate, lithium bicarbonate, sodiumbicarbonate, sodium bicarbonate, potassium bicarbonate, lithiumcarbonate, sodium carbonate, potassium carbonate, lithium sulfate,sodium sulfate, potassium sulfate, lithium phosphate, sodium phosphate,potassium phosphate, lithium sulfite, sodium sulfite, and potassiumsulfite.

The catalyst for the ammonolysis reaction of alkali isethionate in thepresence of alkali ditaurinate and alkali tritaurinate can be onecomponent or a combination of two or more components. Preferablecatalysts are alkali hydroxide and the most preferable catalyst issodium hydroxide.

The amount of catalyst used is not limited, but is usually from 0.01 to10 in molar ratio of the catalyst to alkali isethionate. The ratio ispreferably in the range of 0.01 to 1, more preferably 0.1 to 0.5, mostpreferably 0.2 to 0.3. A suitable amount of catalyst can be selected bythose skilled in the art for the ammonolysis reaction to complete indesired time.

As a catalyst, alkali hydroxide is introduced into the reaction systemand additional ammonium isethionate is required to neutralize the strongbase. The result is an increased accumulation of alkali in the cyclicprocess. It is thus preferable to generate the alkali hydroxide withinthe production unit. A convenient way is to split a mixture of alkaliisethionate and alkali ditaurinate in the mother liquor into an acidiccomponent, a mixture of isethionic acid and ditaurine, and an alkalihydroxide component, by using bipolar membrane electrodialysis. Themixed acidic solution of isethionic acid and ditaurine is used as anacid after the ammonolysis while alkali hydroxide is used as a catalystfor the ammonolysis reaction.

The cyclic process according to the present invention affords taurine ina yield of greater than 90%, to nearly quantitative, and generates nowaste other than a small amount of purge from the cyclic system.

Moreover, the taurine product produced according to the presentinvention does not contain any inorganic contaminants, such as alkalisulfate or alkali halide, which is present in the commercially availableproducts from existing industrial processes.

The process according to the present invention can be carried outdiscontinuously, semi-continuously, and continuously.

DESCRIPTION OF THE DRAWING

FIG. 1 illustrates one embodiment of a flowchart for producing taurinefrom ammonium isethionate.

EXAMPLES

The following examples illustrate the practice of this invention but arenot intended to limit its scope.

Example 1

To a 2-L autoclave are added 1200 mL of 24% ammonia solution, 296 g ofsodium isethionate, and 2 g of sodium hydroxide. The solution is heatedto 260° C. for 2 hours under autogenous pressure. After cooling, 286.2 gof ammonium isethionate is added and ammonia is removed by boiling tobring the pH of the solution to pH 6.5. After heating to remove excessammonia, concentrating and cooling to room temperature, a suspension ofcrystalline taurine is obtained. Taurine is recovered by filtration anddried to 189.3 g. Taurine is recovered in a yield of 75.7%.

Example 2

To the mother liquor of Example 1 is added 340 g of gaseous ammonia andtotal volume is adjusted to 1500 mL with deionized water, followed byaddition of 12.4 g of sodium hydroxide. The solution is placed in a 2-Lautoclave and is subjected to ammonolysis reaction and treatment withammonium isethionate as described in Example 1.

Taurine, 241.2 g after drying, is obtained in a yield of 96.2% on thebasis of ammonium isethionate used.

Examples 3 to 7

The mother liquor after isolation of taurine, after being saturated withammonia, is repeatedly subjected to the ammonolysis reaction in thepresence of 15 g of sodium hydroxide 5 times for an overall yield oftaurine of 96.4% on the basis of ammonium isethionate used.

It will be understood that the foregoing examples, drawing, andexplanation are for illustrative purposes only and that variousmodifications of the present invention will be self-evident to thoseskilled in the art. Such modifications are to be included within thespirit and purview of this application and the scope of the appendedclaims.

What is claimed is:
 1. A cyclic process for producing taurine fromammonium isethionate, comprising: (a) adding ammonia to a solution of amixture of alkali isethionate, alkali ditaurinate, and alkalitritaurinate, and subjecting the solution to an ammonolysis reaction inthe presence of one or a combination of two or more catalysts to yield amixture of alkali taurinate, alkali ditaurinate, and alkalitritaurinate. (b) adding ammonium isethionate to the solution of (a)before or after removal of ammonia to yield alkali isethionate andammonium taurinate; (c) decomposing ammonium taurinate by heating andremoving ammonia from (b) to obtain a crystalline suspension of taurinein a solution of alkali isethionate, alkali ditaurinate, and alkalitritaurinate; then (d) separating taurine by means of solid-liquidseparation and to provide a mother liquor containing a mixture of alkaliisethionate, alkali ditaurinate, and alkali tritaurinate; (e) returningthe mother liquor of (d) to (a) for further ammonolysis reaction.
 2. Theprocess according to claim 1, wherein ammonium taurinate is decomposedto taurine by heating from 75° C. to 150° C.
 3. The process according toclaim 1, wherein ammonia released in step (c) from the thermaldecomposition of ammonium taurinate is removed from solution underreduced, normal, or increased pressure.
 4. The process according toclaim 1, wherein the basic solution of reacting ammonium isethionatewith alkali taurinates in step (c) becomes neutral in a pH range of 6 to8 after thermal decomposition and ammonia removal.
 5. The processaccording to claim 1, wherein the amount of ammonium isethionate inrelation to alkali taurinates in the ammonolysis solution of step (c) isfrom 0.1 to 10 on the molar basis.
 6. The process according to claim 1,wherein the yield of taurine from ammonium isethionate is from 90% tonearly quantitative.
 7. (canceled)
 8. The process according to claim 1,wherein the taurine product of step (d) does not contain alkali sulfateor alkali halide as impurities.
 9. The process according to claim 1,wherein one or a combination of two or more catalysts for theammonolysis reaction is selected from the alkali salts of hydroxide,carbonate, sulfate, sulfite, phosphate, nitrate, or carboxylate.
 10. Theprocess according to claim 1, wherein the alkali taurinate, alkaliditaurinate and alkali tritaurinate are lithium, sodium, or potassiumsalts thereof.